The psoas muscle is a long, deep muscle joining the lower spine to the thigh, one on each side. It attaches to the lumbar vertebrae and their discs, runs through the pelvis and ends near the top of the thigh bone. There it merges with the iliacus to form the iliopsoas, one of the main muscles that lift your thigh as you walk or climb stairs. The psoas also steadies the lower back when you sit.
The psoas is anchored to the lumbar spine and squeezes it hard when it contracts
A 1992 study by Bogduk and colleagues found that the muscle barely bends the lower spine but, fully contracted, presses the lumbar segments together with severe force. The StatPearls clinical reference lists low back pain from compressed discs among the effects of an irritated psoas. Tightness is a different claim. A 1988 study that followed about 600 young men through military service found no link between a tight psoas and back pain, and a 2002 study of 600 adults found none with iliopsoas length or with how far the pelvis tilts forward.
An irritated psoas tends to flare as you get up after sitting
Irritation of the muscle is sometimes called psoas syndrome, and it puts pain in the groin or hip, sometimes with an ache where the lower back meets the buttock. Sitting holds the muscle short, and StatPearls notes that standing up from a seat commonly sets the pain off. An afternoon of gardening, bent at the hips, can end the same way. It is rare, and most often brought on by overusing the hips or a sports injury.
The kneeling hip flexor stretch misses the psoas if your lower back arches
An NHS physiotherapy leaflet has you keep the back straight and the tailbone tucked under while easing the hip of the kneeling leg forward, stopping at a gentle stretch in the front of that hip. A physical therapist quoted by Cleveland Clinic warns that arching the back takes the stretch off the psoas, and that an irritated muscle tolerates stretching badly. Start gently and stop if it hurts. Better still, have the pain checked first, as Cleveland Clinic advises.
Pain in the same spot can start in the hip joint or the lower spine
Hip arthritis is one look-alike, with pain mostly in the groin or thigh, sometimes worse after sitting. A disc pressing on an upper or middle lumbar nerve root can send pain into the groin or down the front of the thigh, though most lumbar disc herniations happen at the two lowest levels. Inflammation of the sacroiliac joint, where the spine meets the pelvis, can also spread pain into the hips and worsen after long sitting.
Less often, the muscle itself becomes infected. An abscess there is rare and often diagnosed late, and fever is one of its more common signs.
A Sync specialist measures how the hips and spine move, and a doctor names the cause
Alongside checks on how the hips move, SpinalSync tests each segment of the spine on its own and shows the readings on screen as they are taken. Adaptive piezoelectric biosensors then deliver the adjustment at a controlled force, angle and depth, so it does not vary by practitioner or by day, though manual adjustment is still used when it is the right call. MyoSync works with soft tissue and fascia. The aim is to support comfort and movement, with repeat measurement showing what has changed. The Sync does not diagnose, prescribe medication, inject, operate, or provide or read imaging, and a Sync specialist says early when something needs a doctor. Our conditions page lists what else we assess.
Common questions about the psoas muscle
Mostly deep in the groin or at the front of the hip, sometimes with an ache low in the back just above the buttock. It commonly flares as you stand up after sitting. Hip arthritis and some disc problems can hurt in the same places, so the spot alone does not reveal the cause.
Not reliably on your own, because both tend to hurt in the groin and both can be worse after sitting. A doctor examines how the hip moves and decides whether imaging is needed. The NHS lists osteoarthritis as a possible cause of hip pain in people over 45, especially when walking makes it worse.
Sitting keeps the hip bent and the psoas short, and StatPearls names long periods of sitting as a cause of cramping and pain in the muscle. A physical therapist quoted by Cleveland Clinic adds that it can weaken from disuse, not only stiffen. Two studies of about 600 people each found no link between psoas tightness or length and back pain, though.
No. The Sync does not diagnose, prescribe medication, inject, operate, or provide or read imaging, so pinning pain on the psoas is a doctor's call. A Sync specialist measures how your hips and lower back move, monitors change and supports comfort and movement, using gentle, instrument-guided, low-force input for anyone who would rather not be adjusted by hand.
Written by the Aphyx Content team, reviewed by the clinical team at The Sync. Published 10 November 2026. Last updated 10 November 2026.